RF amplifiers normally achieve their maximum efficiency while being at saturation level. In many wireless applications, controlling output power as a function of receiving level is required. Withdrawal from saturation level will reduce efficiency. According to conventional solutions, the power stage is designed to handle the highest expected power, leading to lower efficiency at lower output power levels due to high quiescent currents.
One of the conventional ways to eliminate this problem is to control the DC supply of the power amplifier as a function of the power level. This solution is described for example, in U.S. Pat. No. 6,437,641, which discloses circuitry for dynamically enhancing the operating voltage of an RF amplifier. The resulting input drive to the PA is increased, thereby pushing its output well into saturation and handles the signal clipping by instantaneously enhancing the power supply voltage. However, additional active circuitry is required for such enhancement.
The efficiency of non-linear power amplifiers (which do not operate under class A conditions) is usually reduced with output power reduction. In many cases, especially where increased linearity is not needed, this behavior might be avoided. Other conventional ways of controlling efficiency are: using variable power supplies or enhanced dynamic loading techniques, such as a Linear Nonlinear Component (LINC) amplifier (that amplifies a signal which has amplitude variations that are generated by two or more signals, which vary only in their relative phases. The vector sum of the two signals can represent any amplitude) or an amplifier that operates in Doherty configuration (described for example, in U.S. Pat. No. 2,210,028).
Still, the methods described above have not provided satisfactory solutions to the problem of improving the efficiency of power amplifiers operated under large peak-to-average ratio input signals.
It is an object of the present invention to provide a method for efficiently controlling the current consumption of the PA for each level of output transmitting power.
It is another object of the present invention to provide a method for efficiently controlling the impedance at the output of the RF path for increasing the RF large signal gain of the amplifier without increasing the current consumption of the PA.
It is another object of the present invention to provide circuitry for efficiently controlling the PA current consumption, gain and output power independently.
Other objects and advantages of the invention will become apparent as the description proceeds.